Refrigeration & Air-Conditioning Practice Set-3

May 18, 2021

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1. The condition of refrigerant after passing through the condenser in a vapour compression system is

Wet vapour

Saturated liquid

Dry saturated vapour

Superheated vapour

2. In actual air-conditioning applications for R-12 and R-22, and operating at a condenser temperature of 40° C and an evaporator temperature of 5° C, the heat rejection factor is about

2.15

1.25

5.12

3. In a flooded evaporator refrigerator, an accumulator at suction of compressor is used to

Collect vapours

Superheat the vapour

Detect liquid in vapour

Collect liquid refrigerant and prevent it from going to compressor

4. The freezing point of sulphur dioxide is

-77.7°C

-56.6°C

-75.2°C

-135.8°C

5. The capillary tube, as an expansion device, is used in

Domestic refrigerators

Water coolers

All of these

Room air conditioners

6. The refrigerant after condensation process is cooled below the saturation temperature before throttling. Such a process is called

Super-cooling

Sub-cooling or under-cooling

Normal cooling

None of these

7. Most thermostatic expansion valves are set for a superheat of

20°C

5°C

15°C

10°C

8. A bootstrap air cooling system has

Four heat exchangers

Two heat exchangers

Three heat exchangers

One heat exchanger

9. In a lithium bromide absorption refrigeration system

Water is used as a refrigerant and lithium bromide as an absorbent

Lithium bromide is used as a refrigerant and water as an absorbent

Ammonia is used as a refrigerant and lithium bromide as an absorbent

None of these

10. The C.O.P. of a refrigerator working on a reversed Carnot cycle is (where T₁ = Lowest absolute temperature, and T₂ = Highest absolute temperature)

(T₁ - T₂)/T₁

T₂/ (T₂ - T₁)

(T₂ - T₁)/T₁

T₁ / (T₂ - T₁)

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11. The change in evaporator temperature in a refrigeration cycle, as compared to change in condenser temperature, influences the value of C.O.P.

Less

Unpredictable

Equally

12. The bank of tubes at the back of domestic refrigerator is

Capillary tubes

Refrigerant cooling tubes

Evaporator tubes

Condenser tubes

13. Critical temperature is the temperature above which

Water will never evaporate

A gas will immediately liquefy

A gas will never liquefy

Water will evaporate

14. The curved lines on a psychrometric chart indicates

Relative humidity

Wet bulb temperature

Dry bulb temperature

Dew point temperature

15. The general rule for rating refrigeration systems (excepting for CO₂ system) is to approximate following h.p. per ton of refrigeration

1 to 2 h.p. per ton of refrigeration

0.5 to 0.8 h.p. per ton of refrigeration

2 to 5 h.p. per ton of refrigeration

0.1 to 0.5 h.p. per ton of refrigeration

16. The minimum temperature to which water can be cooled in a cooling tower is

Wet bulb temperature of air

Dry bulb temperature of air

Dew point temperature of air

Ambient air temperature

17. A thermostatic expansion valve in a refrigeration system

Is suitable only for constant load systems

Ensures the evaporator completely filled with refrigerant of the load

Maintains different temperatures in evaporator in proportion to load

None of the above

18. Highest temperature encountered in refrigeration cycle should be

Above critical temperature

Much below critical temperature

At critical Temperature

Near critical temperature of refrigerant

19. A human body feels comfortable when the heat produced by the metabolism of human body is equal to the

(A) Heat dissipated to the surroundings

(B) Heat stored in the human body

(D) Difference of (A) and (B)

20. If a heat pump cycle operates between the condenser temperature of +27°C and evaporator temperature of -23°C, then the Carnot COP will be

0.2

1.2

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21. The domestic refrigerator uses following type of compressor

Axial

Miniature sealed unit

Centrifugal

Piston type reciprocating

22. Rating of a domestic refrigerator is of the order of

40 tons

0.1 ton

5 tons

10 tons

23. Which of the following cycles uses air as the refrigerant?

Bell Coleman

Carnot

Stirling

Ericson

24. A reversible engine has ideal thermal efficiency of 30%. When it is used as a refrigerating machine with all other conditions unchanged, the coefficient of performance will be

1.33

3.33

2.33

4.33

25. The vapour compression refrigerator employs the following cycle

Rankine

Reversed Rankine

Reversed Carnot

Carnot

26. When the temperature of the surrounding is higher than the temperature of the body, then the heat loss by convection from the body to the surrounding will be

Negative

Zero

None of these

Positive

27. The boiling point of ammonia is

-77.7°C

-10.5°C

-30°C

-33.3°C

28. The atmospheric air at dry bulb temperature of 15°C enters a heating coil maintained at 40°C. The air leaves the heating coil at 25°C. The bypass factor of the heating coil is

0.4

0.6

0.376

0.67

29. Mass flow ratio of NH₃ in comparison to Freon-12 for same refrigeration load and same temperature limits is of the order of

1: 9

9: 1

1: 3

1: 1

30. Which of the following statement is correct?

(A) The human body can lose heat even if its temperature is less than the atmospheric temperature.

(B) The increase in air movement increases the evaporation from the human body.

(D) Both (A) and (B)

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31. The value of C.O.P in vapour compression cycle is usually

Equal to unity

Always less than unity

Any one of the above

Always more than unity

32. The operating pressure for refrigerating units using R-12 as a refrigerant is

8 bar

15 bar

2 bar

30 bar

33. A certain refrigerating system has a normal operating suction pressure of 10 kg/cm gauge and condensing pressure of about 67 kg/cm. The refrigerant used is

Brine

Ammonia

Carbon dioxide

Freon

34. Freon group of refrigerants are

Toxic

Non-inflammable and toxic

Nontoxic and non-inflammable

Inflammable

35. For obtaining high COP, the pressure range of compressor should be

Low

High

Any value

Optimum

36. On the pressure-enthalpy diagram, condensation and desuperheating is represented by a horizontal line because the process

Involves no change in volume

Takes place at constant entropy

Takes place at constant pressure

Takes place at constant temperature

37. In a refrigeration system, the expansion device is connected between the

Receiver and evaporator

Condenser and receiver

Evaporator and compressor

Compressor and condenser

38. Cooling water is required for following equipment in ammonia absorption plant

Condenser

Absorber

Evaporator

Condenser, absorber and separator (rectifier)

39. In a refrigeration system, heat absorbed in comparison to heat rejected is

Same

More for small capacity and less for high capacity

Less

40. Which of the following is not a desirable property of a refrigerant?

Good electrical conductor

Low boiling point

Large latent heat

High risibility with oil

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A Demrot is the founder of VideRime Online Learning, a leading engineering website. He did his BE Civil and M.Tech Structure from RGPV University, Bhopal and has been working as an Assistant Professor in a reputed college.

Refrigeration & Air-Conditioning Practice Set-3

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